None.
The present invention relates to automotive engine analyzers. In particular, the present invention is an engine analyzer which automatically selects DIS secondary ignition signals for digitization and display.
Engine analyzers are used by automotive technicians and mechanics to test the operation of an automobile engine and to assist the technician or mechanic in evaluating the operation of an engine and identifying sources of poor performance or engine malfunction. The engine analyzer includes test leads, probes, and other sensors which are connected to the engine to sense signals or operating parameters of the engine.
One important subsystem of an automobile engine which is tested is the ignition system. This system delivers electrical voltages to spark plugs to cause ignition of a compressed fuel and air mixture at or near the top of the compression stroke of the piston in each cylinder. The firing of the spark plug ignites the fuel and air mixture, causing an explosion which drives the piston downward to produce the power stroke. There are a number of different components within the ignition system which can result in the failure to produce a spark at a particular cylinder or the production of a spark which is less than optimal. For example, a spark plug may be defective, or may have an improper spark gap; a spark plug wire may be detective or failing; an ignition coil may fail; or components of the distributor or electronic ignition control circuitry may be failing or malfunctioning. Many of these problems can be detected by a skilled mechanic by viewing displays of secondary ignition voltage waveforms. These waveforms show secondary voltage applied to the individual spark plugs as it varies as a function of time. Different component failures cause characteristic changes to the shape and appearance of waveforms.
Originally, automotive engine analyzers used analog oscilloscope displays to display ignition waveforms for the mechanic. In 1982, Bear Automotive Service Equipment Company introduced the Bear ACE engine analyzer, which featured a single raster scan display for displaying all information, including simulated representations of engine ignition waveforms. The ACE analyzer digitized time varying signals, such as primary and secondary ignition signals, stored the digital samples, and subsequently displayed the waveform(s) on the raster scan display based upon those digitized samples. A digital engine analyzer in which waveforms are digitized and then displayed became the industry standard during the 1980""s and has continued to be the industry standard today.
For many decades, most automobile engines used a distributor to produce the secondary voltage pulses and to distribute those pulses to the individual spark plugs. In the 1970""s, solid state ignition systems began to be used in place of the mechanical breaker points traditionally used in distributor type ignition systems. The distributor type ignition system uses a single ignition coil to produce the voltage pulses and a rotor which distributes the secondary voltage pulses in sequence to the spark plug wires connected to the spark plugs. In the 1980""s, distributorless ignition systems (DIS) were introduced to replace the traditional distributor type ignition systems. DIS ignition systems typically use one ignition coil for each pair of spark plugs. The spark plug pairs are selected so that one spark plug will fire when its cylinder is at the top of the compression stroke, while the other spark plug fires while its cylinder is at the top of the exhaust stroke. An electronic control circuit controls the flow of primary current through the primary winding of the DIS ignition coil and interrupts the flow of primary current at the appropriate time to induce a secondary voltage pulse in the secondary winding of the DIS ignition coil. A spark plug is connected to each end of the secondary winding of the DIS ignition coil. One of the two spark plugs, therefore, will fire from a positive going voltage pulse with respect to ground, while the other spark plug of the pair fires with a negative going pulse with respect to ground.
The introduction of DIS ignition systems presented a new set of challenges to designers of automotive engine analyzers. The engine analyzer needed to be adaptable to handle both distributor type ignition systems as well as DIS systems. The distributor type ignition system required only a single secondary voltage probe, which would clip onto the high voltage lead from the secondary winding of the single ignition coil to the center terminal of the distributor. Secondary voltage pulses would be produced in succession in the high voltage lead from the coil to the distributor, and those pulses would be distributed to the individual spark plug wires by the rotor of the distributor. A #1 probe from the engine analyzer would be connected to the #1 spark plug wire, in order synchronize the operation of the engine analyzer with the engine. By sensing the #1 pulse as well as each secondary voltage pulse (or each primary voltage pulse), the engine analyzer could produce a cylinder count which would accurately reflect which cylinder in the firing order of the engine was currently firing.
With a DIS engine having pairs of spark plugs sharing ignition coils, there is no longer a single lead from the ignition coil to a distributor. In order to sense secondary voltage in a DIS engine, therefore, individual probes need to be connected to the individual spark plug wires. The engine analyzer must selectively invert the signals from half of the cylinders, so that all of the ignition voltage pulses appear on the display screen with the same polarity. Typically, ignition waveforms are displayed so that the secondary voltage pulse is a positive going pulse. This requires that any negative going pulses which are to be displayed must be inverted. Finally, in order to synchronize the engine analyzer with the engine to identify the proper cylinder as they fire, the #1 cylinder power firing event must be identified. During each complete engine cycle, the #1 spark plug wire will receive two pulses: one during a power firing event, and one during an exhaust or wasted firing event. The #1 cylinder power firing event needs to be identified.
In the past, engine analyzers have typically used two sets of leads for connection to the spark plug wires of a DIS engine. These leads are typically color coded and may be, for example, a set of black leads and a set of red leads. The instructions to the mechanic require that all of one set of leads are connected to spark plug wires of one polarity, and the other set of leads are connected to spark plug wires for the opposite polarity. For example, if all black leads are connected to positive firing spark plug wires, then all red leads are connected to negative firing spark plug wires.
The requirement that particular leads be connected to particular polarities complicates the set up of the engine analyzer when analyzing a DIS engine. Even when the mechanic makes the proper connections, problems can still be encountered. For example, replacement ignition coils for DIS engines may be wound in an opposite direction from the original parts. When replacing a detective coil with a replacement coil, a reversal of the polarities of the respective cylinders may occur. Although the engine will operate properly regardless of the polarity of by the ignition coil, the engine analyzer will not. If polarities are reversed on certain leads, the signals derived will have incorrect polarities when processed and displayed by the engine analyzer. This can also result in misidentification of the proper #1 cylinder firing event.
More recently, ignition systems have been developed in which a single coil is used for each cylinder (a so called xe2x80x9ccoil per cylinderxe2x80x9d) ignition system. In addition to the distributor type ignition systems, the engine analyzer must also be capable of working with engines having either a pair of cylinders per coil or a single cylinder per coil. It is desirable to use the same set of leads for both ignition systems with a coil or coil pack for a pair of cylinders, as well as ignition systems with a coil per cylinder.
The present invention processes and selects secondary ignition signals while simplifying the connection of leads required to be made by the mechanic. Two sets of secondary ignition signal leads are provided, and one lead is connected to sense the secondary voltage pulse supplied to each spark plug. With an engine having a coil for each pair of cylinders, a lead from one set is connected to one of the two spark plug wires and the other lead is connected to the opposite spark plug wire (i.e., on opposite sides of the ignition coil). There is no requirement, however, that all spark plugs of one polarity be connected to one set of leads and all of the opposite polarity be connected to the other set.
The engine analyzer receives the secondary signals produced by both sets of leads. For each cylinder firing, the signal strength on each lead set in both positive and negative directions is determined. Based upon the relative signal strengths from the leads in positive and negative directions during each cylinder firing event, the engine analyzer determines which lead and polarity should be selected when that cylinder fires in the future. The engine analyzer routes the secondary voltage signal, from the appropriate lead set with the appropriate polarity to an analog-to-digital converter, which digitizes the secondary voltage waveform for subsequent analysis or display.